Abstract
Aim
To investigate the effects of strain rate and mineral level on the stress at failure, stiffness and toughness of whole bones.
Methods
40 ovine femurs were harvested and subjected to either slow [8.56 × 10−3 s−1 (± 1.42 × 10−3 SD)] or dynamic [17.14 s−1 (± 8.20 SD)] loading. Half the bones were demineralised by 20% compared to the original mineral content. These were allocated evenly between the high and low strain rate groups. Dynamic loading was achieved by custom designed comminution device. Slow rate testing was carried out on a Zwick/Roell z005 testing machine.
Results
Strain rate was found to increase the Young's modulus in both the normal and demineralised bone. Additionally the toughness of the bones at failure was found to reduce with increasing strain rate. When comparing bone of normal quality the stress at failure was found to increase with strain rate. However, this effect was greatly reduced when comparing the effect of strain rate on the stress occurring in demineralised bones.
Discussion
These results show that bone has an ability to withstand higher than normal stresses if these are applied quickly and for a short duration (such as would occur in a traumatic event). This ability is greatly reduced when the bone is of reduced mineral content, such as is found in aged or diseased bone.
